1. Technical Field
The present invention relates to an image display apparatus and a viewing angle compensation method for compensating an optical phase difference resulting from birefringence associated with liquid crystal molecules that form a liquid crystal panel used in the image display apparatus.
2. Related Art
There has been a known projector including a light source, a light modulator that modulates the light flux emitted from the light source in accordance with image information, and a projection optical unit that enlarges and projects the modulated light flux on a screen or any other suitable projection surface. A known example of the light modulator is a liquid crystal light valve including a liquid crystal panel and a pair of polarizing elements that sandwich the liquid crystal panel, the liquid crystal panel including a liquid crystal layer having liquid crystal molecules sealed between a pair of substrates and modulating a light flux incident thereon.
In a TN (Twisted Nemetic) liquid crystal light valve, the liquid crystal molecules are twisted between the substrates that sandwich the liquid crystal layer when no voltage is applied to the liquid crystal layer. In this case, the polarization direction of linearly polarized light having passed through the light flux incident-side polarizing element is rotated in accordance with the twisted arrangement of the liquid crystal molecules. The linearly polarized light whose polarization direction has been rotated passes through the light flux exiting-side polarizing element, which along with the light flux incident-side polarizing element forms a crossed-Nicol arrangement in a typically used normally white (NW) liquid crystal light valve, resulting in a bright state.
On the other hand, when a sufficient voltage is applied to the liquid crystal layer, the orientation of the liquid crystal molecules becomes perpendicular to the substrates that sandwich the liquid crystal layer, and the polarization direction of the linearly polarized light having passed through the light flux incident-side polarizing element is not rotated. As a result, in the NW liquid crystal light valve, the linearly polarized light is blocked by the light flux exiting-side polarizing element, resulting in a dark state. On the other hand, in a normally black (NB) scheme, since the directions of the transmission axes of a pair of polarizing elements are parallel to each other, the bright and dark states are reversed.
When light is incident on a NW liquid crystal light valve, which is configured as described above, obliquely with respect to a normal to the light flux incident-side substrate of the pair of substrates that sandwich the liquid crystal layer, birefringence associated with the liquid crystal molecules in the vicinity of that substrate disadvantageously cause part of the light to pass through the light flux exiting-side polarizing element (leakage of light from the liquid crystal light valve). As a result, the contrast of an image to be formed disadvantageously decreases.
To address the problem, there has been a known solution in which a compensating element that cancels the effect of birefringence associated with the liquid crystal molecules and compensates the optical phase difference resulting from the birefringence (see JP-A-2006-259256, for example). In the projector described in JP-A-2006-259256, the viewing angle characteristics of a liquid crystal light valve are improved by providing the compensating element (viewing angle compensator) between a liquid crystal panel and a light exiting-side polarizer. That is, the optical phase difference resulting from the birefringence associated with the liquid crystal molecules, the effect of the birefringence, is cancelled by providing an antiphase compensating element.
It is noted that the orientation (arrangement) of the liquid crystal molecules located in the vicinity of the substrates that sandwich the liquid crystal layer is not uniform when a voltage is applied, in other words, the viewing angle characteristics of the liquid crystal panel are not uniform as a whole. As a result, the method used in the projector described in JP-A-2006-259256, in which a single compensating element that covers the liquid crystal layer and has a compensation direction aligned with a predetermined direction is used to improve the viewing angle characteristics of the entire liquid crystal panel, does not work, resulting in a portion where the viewing angle is compensated and a portion where the viewing angle is not compensated. As a result, a NW liquid crystal light valve suffers from black unevenness or in-plane contrast unevenness in the dark state. In particular, when an inexpensive liquid crystal panel including no lens array in which tiny lenses that guide the light to be incident on black matrices to the liquid crystal layer are arranged in correspondence with pixels is used, black unevenness more likely occurs than in a case where a liquid crystal panel including the lens array.